Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters and other images to be printed upon the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
In one prior art design, the inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) an orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice in the nozzle member and onto the paper.
Two patents that describe examples of printhead portions of an inkjet printhead that may be improved by the present invention are U.S. Pat. No. 5,638,101 entitled High Density Nozzle Array for Inkjet Printhead, by Brian Keefe et al., and U.S. Pat. No. 5,278,584, entitled "Ink Delivery System for an Inkjet Printhead," by Brian Keefe et al., which are assigned to the present assignee and incorporated herein by reference. In U.S. Pat. No. 5,278,584, ink is fed from an ink reservoir to each vaporization chamber through an ink channel formed in a barrier layer between the substrate and the nozzle member. The ink channels in the barrier layer generally have ink entrances running along two opposite edges of the substrate so that ink flowing around the edges of the substrate gain access to the ink channels and to the vaporization chambers. A disadvantage of this type of prior art inkjet printhead design is that internal contaminants may plug the ink flow path in the printhead. Consequently, the flow of ink may become restricted or shut off entirely thereby preventing the droplet of ink from being ejected onto the paper. Further, the energization of a heater element in one vaporization chamber may affect the flow of ink into a nearby vaporization chamber, thus producing cross-talk. Cross-talk affects the amount of ink emitted by an orifice upon energization of an associated element.
One method of keeping particles from plugging the ink flow path is to build a very clean inkjet print cartridge, i.e., an inkjet print cartridge with no foreign particles. However, eliminating small particles produced in the manufacture of an inkjet print cartridge is difficult and expensive. Another particle tolerant configuration uses multiple inlet channels into each vaporization chamber. Thus, when one inlet channel is plugged by a foreign particle, ink can still flow into the vaporization channel through other inlet channels. However, the performance of the multiple channel configuration changes when one channel is plugged, thereby degrading the print quality of the inkjet printhead.
Another particle tolerant configuration is described in U.S. Pat. No. 5,638,101, which uses enlarged areas or "barrier reefs" formed near the entrance of each ink channel to constrict the entrance of the ink channels to help filter large foreign particles. In addition, relatively narrow constriction points, known as pinch points, are included in the ink channels to provide damping during refill of the vaporization chambers after firing to help reduce cross-talk. However, barrier reefs can be knocked off during processing thus becoming useless, or worse, becoming a contaminant themselves. Further, using pinch points and barrier reefs within the ink channels lengthens the ink channel, which requires an increase in the substrate area.
Consequently, what is needed is a particle tolerant printhead architecture for an inkjet print cartridge.